Using a needle-free injection device to inject medicated fluid into the body is well known in the art. For instance, U.S. Pat. No. 6,673,035 discloses a needle-free injector that administers medication as a fine, high velocity jet. This high velocity jet is delivered to the injection site under sufficient pressure to enable the liquid jet to pass through the skin without having to puncture the skin.
U.S. Pat. No. 6,673,035 discloses a device that includes two main sections. The first section contains a disposable cartridge that carries the fluid medication that will be injected into the body. The second section is a needle-free injecting assembly that is designed to pressure inject the fluid into the body at a specified location.
Using the needle-free injector of U.S. Pat. No. 6,673,035 enables medication to be administered without all of the problems associated with using a traditional syringe and needle puncturing the skin. Limitations on the device disclosed in U.S. Pat. No. 6,673,035, however, exist. For instance, the two main sections of the device are placed co-linear. Therefore, the device can be difficult to use, especially by a patient lacking dexterity, because it occupies a great deal of space in one direction. Another challenge with the device is the cartridge includes a movable piston that should change position inside of the cartridge as fluid is withdrawn from the cartridge. Such pistons can, however, fail to move in various situations because of adhesion or static friction between the piston and the cartridge wall. U.S. Pat. No. 6,673,035 does disclose initially displacing the movable piston during installation of the cartridge, however, adhesion or static friction between the piston and the cartridge wall can still be a problem especially during subsequent times of use.
In addition, fluid leakage and power conservation can be problems with prior needle-free injectors.